ABSTRACT
The Riachuelo Sanitation Scheme in Buenos Aires (Argentina) foresees the execution of 12km of outfall tunnel (hydraulic capacity of 27 m³/s) into the La Plata River, one of the largest estuaries in the world. The tunnel lining design had to allow for very demanding structural requirements since during the project operation the internal pressures inside the tunnel may exceed the hydrostatic external pressures, up to 1.5 bar, throughout a service life of 100 years.
An extensive analysis of possible design alternatives was carried out, the solution of a single-pass 4.3m ID segmentally lined tunnel being finally implemented. Such solution eliminated the need for a secondary cast-in-situ lining which is commonly adopted for similar cases.
This paper describes the innovative tunnel lining design conceived to guarantee high performance levels of structural strength and durability. This considers a load-sharing scheme between radial bolts and circumferential dowels, backed up with extensive laboratory and full scale testing of the mechanical connections, detailed assessment of tensile and shear loads (from bolts and dowels), transmission into the entire reinforcement, crack width, joint opening and construction tolerances, to meet the foreseen structural mechanisms. Geotechnical monitoring and back analysis program was implemented to confirm critical design assumptions.
The removal of the internal lining led to additional conveyance capacity, lower pumping heads and a simplification in the construction process reducing significantly health and safety risks.
